Corrugated metal pipe is distinguished from other pipes in that it comprises corrugations, which consist of successive bends in the surface of the pipe. The corrugations in the walls of the CMP add stiffness and strength to the pipe. They are used in many projects for a variety of purposes, such as for culverts, storm sewers, subdrains, spillways, underpasses and conveyor conduits. They are also often used to re-line damaged preexisting pipe.
CMP acts as a conduit for fluids, such as sewage and rainwater, and tends to wear and corrode at the bottom of the flow-line of the pipe after years of service. The extent of deterioration depends primarily on soil conditions and the acidity of the water flow. In some instances, this condition can cause sinkholes to form that allow water to escape during heavy rain and destroy property. In such cases, it would be prohibitively expensive and time-consuming to repair the entire pipe and it would not stabilize and fill the void areas exterior to the pipe.
Chapter 10 of the Handbook of Steel Drainage & Highway Construction Products, 2nd Canadian ed., Corrugated Steel Pipe Institute, 2007, which is incorporated herein by reference in its entirety, describes the preexisting methods for repairing CMP: In-place installation of concrete invert; Slip line with slightly smaller diameter pipe or tunnel liner plate; Inversion lining, Shortcrete lining; cement mortar lining; and patching. Of these methods, patching is the most inexpensive and adaptable to various sizes and shapes of CMP.
The known methods for patching CMP include the use of polymer and concrete patching compounds or mechanically attaching or welding similar CMP to the damaged area. However, merely patching a damage area of the CMP using only a polymer or concrete provides insufficient structural integrity to the damaged area. The application of concrete patching compounds is quite expensive and time consuming and will not address the problem of voids in the earth that have developed due to erosion at the site of the damaged flow-line.
Simply applying polymer directly to the damaged portion is not effective without some form of molding containment. Without molding containment, the polymer will become unwieldy and, if it is an expanding polymer, it will not attain maximum rigidity upon hardening, since pressure is required to maximize bonding strength.
Attaching only a similar CMP to the damaged area is also non-optimal because the attached plate and the preexisting pipes will constitute two separate structures bound only at the point of attachment and therefore will not be sufficiently reinforced or sealed. This will also not address the problem of voids in the earth surrounding the CMP.
Therefore, an improved method is needed for repairing the damaged portion of the flow-line of a CMP that is cost effective and provides a single monolithic patch as well as filling and stabilizing the surrounding voids created in the soil.